Publish a Ruby gem

Naming

In general, the gem name should be the same as the thing you require when using
it. This means using _, and not - to separate multi-word gem names. See the
name your gem guide for more detailed
guidance.

Versioning

Versions should only be changed in a commit of their own, in a pull request of
their own.

This alerts team members to the new version and allows for last-minute scrutiny
before the new version is released. Also, by raising a separate pull request,
we avoid version number conflicts between feature branches.

File layout

We should follow the scheme used by Bundler when creating gems (see this
railscast).

Some points to note:

The version is stored in a file by itself in lib/<gem_name>/version.rb.

The Gemfile references the gemspec for gem dependencies. All gem
dependencies should be specified in the gemspec.

The Gemfile.lock is never committed (it should be in the .gitignore
file).

Releasing gem versions

The default Jenkins build script will automatically detect the presence of a
gemspec file and publish the gem to rubygems.org. See the
Jenkinsfile for govuk-lint
for an example.

Clearing the gemstash cache

When a new gem version is released, it may not be available immediately on Jenkins.
This is due to gemstash, our gem mirror. It caches versions for up to 30
minutes. To force it to clear, run this on apt-1.management in the relevant
environment:

$ sudo docker restart gemstash

To clear the cache for the CI Jenkins instance, run this in integration.